[PATCH v6 net-next 02/14] gro: flushing when CWR is set negatively affects AccECN

chia-yu.chang
2025-11-14T07:14:00Z

From: Ilpo Järvinen <ij@kernel.org>

As AccECN may keep CWR bit asserted due to different
interpretation of the bit, flushing with GRO because of
CWR may effectively disable GRO until AccECN counter
field changes such that CWR-bit becomes 0.

There is no harm done from not immediately forwarding the
CWR'ed segment with RFC3168 ECN.

Signed-off-by: Ilpo Järvinen <ij@kernel.org>
Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
---
net/ipv4/tcp_offload.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
index 2cb93da93abc..fcbf4148919c 100644
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -330,8 +330,7 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb,
goto out_check_final;

th2 = tcp_hdr(p);
- flush = (__force int)(flags & TCP_FLAG_CWR);
- flush |= (__force int)((flags ^ tcp_flag_word(th2)) &
+ flush = (__force int)((flags ^ tcp_flag_word(th2)) &
~(TCP_FLAG_FIN | TCP_FLAG_PSH));
flush |= (__force int)(th->ack_seq ^ th2->ack_seq);
for (i = sizeof(*th); i < thlen; i += 4)
--
2.34.1